Biasi m90f 24s find dhw but no ch?

[scorour]

Hi,
My boiler died beyon economical repair and was given (for free) a Biasi 24s which was manufactured in 2005. It was fitted by a friend of a friend who is in the trade. The installer left believing the problem was with the thermostat but I downloaded the manual and checked the bypass link was in plac, which it was.

What happens is that, the hot water works fine, no problem.

But when the boiler is switched on, the pump sounds like it is in is a cycle, repetitive noise from it (not sure if this is normal), like a humming noise for a second or two, then it stops and humms again, repeating constantly. Whilst this is happening, the needle on the pressure gauge moves in tandem, moves a millimetre or two then drops back when the humming noise stops, so flicking back and forth constantly. (The pump is moving, as removing the cap, it can be seen to move).

Initially on switch on, during the above, the boiler fires up for 5 or 10 seconds, then cuts out.

The power/standy led (led 1) is constantly blinking every two seconds.

I tried the diagnostic, which says to move a dip switch off then on, looking at the two extra led's hidden from thwe front, led 1 and led 3 flash intermittently. The book suggests this is in dhw mode only, even though the dial in on the snowflake (above the off position).

The heating hot water pipe does not get hot (below the boiler, in the boiler it is red hot), it seems to me as if the water cannot be pumped down the pipe, the pipe is open as the temperature gradually slowly warms up as if the hot water is mixing with the cold water.....

Any help would be appreciated, waiting to speak the installer tomorrow, any info would be greatly appreciated.

Thanks.

 

[Agile]

What you have said is not consistant with normal operation but as its so inaccurate I am not confident that its correct!

For example the lights flash every second and not every two seconds!

In diagnostic mode the two greens flash together every second! Not intermittently.

If you move the rear link down one pin towards the front then its in permanent diagnostic mode.

It sounds as if the diverter valve motor is not moving. You can check its wired correctly and then take the head off and see if its moving correctly.

If you hold the diverter valve pin down it should give CH.

The pump working intermittently sounds like a fault!

Tony

 

[mehran]

first off, i am surprised agile did not point that all boilers being fitted today should be condensing model. also "second boiler" have a habit of being nicked


fitting second hand boiler is a false economy IMO.


now... i would look at the dhw flow sensor. it should be just to the right of the gas valve. when a hot water tap is open a little red like should come on. if that little red light is on but no tap is on then your dhw flow switch is stuck on.

if so post back here.

 

[scorour]

Firstly, thanks for the quick replies.

TBH, I know the boiler is not new, but it was free (genuine, not stolen) from a property being demolished, for the sake of the discounted fitting, I thought it was worth trying.

>if that little red light is on but no tap is on then your dhw flow switch is stuck on.

I will work through suggestions, thank you, however, looking at the red led on the top of what I believe to be the dhw flow switch, (a black box to with 3 wires going into it?), the led is on constantly, regardless if the boiler is in the off position, or either of the two on positions?

Thanks again, much appreciated

 

[scorour]

I know this is not the solution, but thought I would would post in case it confirms or denies anything.

If I take the plug (with the 3 wires) out of the dhw flow switch, the ch works. Would this suggest when plugged in, the switch is locked on to dhw, taking it out makes it do ch?

thanks again.

 

[mehran]

if that little red light is on but no tap is on then your dhw flow switch is stuck on.

If I take the plug (with the 3 wires) out of the dhw flow switch, the ch works. Would this suggest when plugged in, the switch is locked on to dhw, taking it out makes it do ch?

thanks again.

bingo. the boiler thinks there is always a tap running.

 

[scorour]

if that little red light is on but no tap is on then your dhw flow switch is stuck on.

If I take the plug (with the 3 wires) out of the dhw flow switch, the ch works. Would this suggest when plugged in, the switch is locked on to dhw, taking it out makes it do ch?

thanks again.

bingo. the boiler thinks there is always a tap running.

Excellent, thanks mehran, I have made a note of the part number from the service manual and will sort it out in the morning......did not realise you were from Hartlepool also

 

[mehran]

haha i did not notice ether. i am the biasi service agent for around here. most likely it just needs to be cleaned.

 

[Agile]

Hold on!

If the DHW flow switch is locked on then its almost certainly NOT faulty!

To check, pull it down so the red light is facing forward and then pull it forward and it will come of the grooved part it clips into. Then the light will go out! If not then it would be faulty but its not!

That then means the magnetic shuttle is jammed!

Its often not so easy to get it unscrewed as a DIY job but thats irrelevant!

Its NOT a DIY job anyway because the gas valve has to be removed to get it out!

You will have to call Mehran to do it for you and he will remove the gas valve and then see why its jammed.

He may choose to replace it but if its mostly intact, I can usually free them up. Sometimes its just dirt or pieces of the magnet have cracked or very often the plastic part is roughly injected and has ridges or projections which I file off to give proper clearances.

In the meantime you can choose CH or DHW by replacing or removing the Hall effect detector. An enterprising cafe owner who I explained that to on the phone, then pulled it forward and activated it with a small magnet whenever he wanted hot water.

Tony

 

[scorour]

Morning, thanks for taking the time to reply both of you. Don't worry, this is not a DIY job, I have no intention of trying to fix it myself....I have a computer business and know my limits, I am merely trying to pinpoint/understand the problem (with excellent help from people from this forum).

 

[scorour]

Just got back home to test taking the switch off as suggested.....If I pull the switch down and remove as described the LED then goes off, this is with the boiler in the off position on the dial.

So sounds like the magentic shuttle is jammed as mentioned?

Thanks again, excellent advice.

 

[dawson666]

The heating hot water pipe does not get hot (below the boiler, in the boiler it is red hot), it seems to me as if the water cannot be pumped down the pipe, the pipe is open as the temperature gradually slowly warms up as if the hot water is mixing with the cold water.....

Have you checked that the heating pipe valve under the boiler is in the open position? It may be a lever valve or a screwdriver slot valve thingy which needs to point in the direction the water is going.